No abstract

Ti(C,N), Cermets, Colloidal processing, Functionally gradient material, SteelIn this work, the colloidal approach was used to promote a gradation in the composition of a cermet, based on the mixture of stainless steel and Ti(C,N) during powder consolidation into a bulk part. The colloidal processing of non-oxides in aqueous media requires an elevated control over the evolution of the surface chemistry of the powders, in order to obtain stable and high concentrated slurries of the mixture of metal/non-oxide ceramic. The advantage of those methods lies on the fabrication of complex microarchitectures where the second phases are intimately and homogeneously dispersed in the microstructure of the composite. Moreover, those techniques allow the processing of fine particles with low compressibility and flowability which difficult conventional powder metallurgical processing. The results shown in this work evidence the feasibility of obtaining continuous functionally graded materials (FGM) through slip casting in porous molds, as well as the relevance of the rheological properties of the composite slurries on the final characteristics of the material.

Abstract. The colloid-chemistry control of metallic powders in aqueous slurries is proposed as a way to prepare Ti powders with small particle size for a better pressing behavior through the spray dry process. The chemical-physic behavior of titanium powders with two different particle size distributions dispersed in water has been studied by measuring the zeta potential as a function of pH, and dispersant concentration. The employment of poly-acrylic dispersants allowed the fabrication of stable slurries with solid contents up to 50 vol% that have been sprayed under different conditions to form agglomerates ranging between 50 and 200 µm. Conditions were selected to achieve spherical agglomerates formed by a broad distribution of particle sizes that shown excellent flowability. Agglomerates were pressed in a uniaxial die to measure the compressibility, showing an improvement in pressing behavior with respect to powders with bigger particle size. The sintering behavior is also improved, as values of 96 % of the theoretical density were obtained for compacts sintered in vacuum at 1100 ºC for 30 minutes.

We present a one-pot process to produce an extremely dense packed YSZ nanostructure that can consolidate at unconventionally low temperature.

In recent years, asymmetric membranes based on mixed ionic-electronic conductors (MIEC) have gained importance in practical gas separations. MIEC ceramic materials show high-energy efficiency and high-temperature resistance, which allows direct integration in industrial processes. Thin layers are supported on porous substrates that provide mechanical strength. In the asymmetric membrane manufacture, the control of support porosity and microstructure is crucial. Colloidal processing is an interesting method that allows controlling the final microstructure in both surfaces and bulk, with high reproducibility. Here, the development of asymmetric membranes with a top functional layer made of Ce 0.8 Gd 0.2 O 1.9 /Ni 2 FeO 4 composite is presented and aims to maximize oxygen permeation and membrane robustness. The porous substrate is prepared by slip casting while the functional layers by screen-printing. The effect of pore former volume and particle morphology were studied. The combination of spherical and flake-like PMMA particles enabled to generate open porosity suitable for fast gas transport.